The invention relates to a process and apparatus employed for the utilization of geothermic energy.
Attempts to utilize the heat contents, the geothermic energy, of dry rocks are well known. According to the "two-well" method water is pressed through one of the wells into the rock while the warmed up water is removed through the other pipe and this may be called an "artificial thermal water production". Of course, there is provided a hydraulic connection between the two wells, e.g. fissures, caves should be formed by blast. In order to achieve that the lower end points of the wells be near each other directional well drilling is applied.
The process according to the Hungarian Patent No. 165.379 is based upon such "artificial thermal water producing" principle, according to which a well structure appropriate for the heat output is suggested, namely, the storage area is a part of the bore hole and is protected by a casing pipe, and separated from the geothermal layer by a blocking piece, while the uptake area is an insulated producing pipe built into the casing. The flow from the annular area toward the producing pipe is provided by a pumping unit.
The disadvantage of the above procedures resides in that they are rather expensive. This is mainly due to the fact that owing to the steady pumping there is a high rate of power consumption and, on the other hand, a heavy insulation is necessary otherwise the medium exploited will return its heat back to fed in medium, still below the terrain.
An efficient insulation has, however, a large space requirement, consequently it will further reduce the cross section of flow which is small anyway. Due to this the power requirement of pumping necessary for the recirculation will further increase. Should a two-well method be applied, where the heating up of the water takes place in direct contact with the natural rocks, the disadvantage is well known that the water exploited, just like in the case of thermal waters, may include undesired minerals and even scale formations may be present.
In an attempt to eliminate the drawbacks associated with the one-well method mentioned above (heat exchange between the external and internal pipes, expensive insulation as well as pumping) proposals have become known, according to which the evaporation heat which is the difference in heat contents between the liquid fed in and the vapor exploited, both of the same temperature, should be utilized.
The rational realization of such processes is strongly impeded by the fact that the pressure of the liquid column is increasing with depth and, as a result, vapor can be produced in a rather small quantity. The same refers to the process published in the Hungarian application for patent No. SE-1710, the essence of which is that liquid is introduced to the inner mantle surface of the steam producing pipe heated up by geothermic energy where it is let run down. Accordingly, a pressure necessary for evaporation is intended to be produced through the entire depth of the well structure.
A drawback of the method lies in its functioning at an almost atmospheric pressure or under vacuum (the surface fittings thereof are conforming thereto; it has a vacuum pump and has no blow-off valve) requiring a considerable vapor rate even in the event of smaller output. As a result, the so called separation tube should be built in in order to separate the vapor-phase, however, the output is limited even in such case.
A further problem in connection with the separation tube resides in the liquid's transfer from the inner surface of the vapor producing pipe, made more difficult by any structural assymetry, into the separation tube and remaining there in this form, as there is no way to return it to its destination.
From the structural point of view it is a disadvantage that the liquid is introduced onto the tube wall by a nozzle which, due to the spraying effect, does not provide for a uniform spreading.
Ultimately, a further drawback resides in that there is no proper heat transfer assured between the well structure and the rocks, therefore, the output, one could expect, is not the best.